The invention relates to Nb-based silicide composite compositions. In particular, the invention relates to Nb-silicide based composite compositions with chemistries that have applications in turbine components.
Turbines and their components, such as but not limited to aeronautical turbines, land-based, turbines, marine-based turbines, and the like, have typically been manufactured using nickel (Ni)-based materials, which are often referred to as xe2x80x9cNi-based superalloysxe2x80x9d. Turbine components, when formed from these Ni-based superalloys, exhibit desirable chemical, physical, and mechanical properties and characteristics under high temperature, high stress, and high-pressure conditions generally encountered in turbines during operation. For example, turbine components in modern jet engines, such as an airfoil, can reach temperatures as high as about 1,150xc2x0 C., which is about 85% of the melting temperatures (Tm) of Ni-based superalloys.
While Ni-based superalloys have provided desirable performance, Ni-based superalloy development has been widely explored and significant recent gains have been few in the past 5 years. Efforts have been made to develop alternative turbine component materials. These alternate materials include niobium (Nb)-based refractory metal intermetallic composites (hereinafter xe2x80x9cRMICxe2x80x9d). A RMIC may possess higher potential application temperatures if the RMIC can be used at temperatures about 80% or more of their melting temperatures, such as greater than about 1700 xc2x0 C.
A RMIC that comprises at least niobium (Nb), silicon (Si), titanium (Ti), hafnium (Hf), chromium (Cr), and aluminum (Al) (hereinafter xe2x80x9cRMICxe2x80x9d) has been proposed for turbine component applications. These silicide-based RMICs exhibit a temperature capability that is higher than current Ni-based superalloys. Exemplary silicide-based RMICs are set forth in U.S. Pat. No. 5,932,033, to Jackson and B.P. Bewlay, entitled xe2x80x9cSilicide Composite with Nb-Based Metallic Phase and Si-Modified Laves-Type Phasexe2x80x9d and U.S. Pat. No. 5,942,055, to Jackson and Bewlay, entitled xe2x80x9cSilicide Composite with Nb-Based Metallic Phase and Si-Modified Laves-Type Phasexe2x80x9d, both of which are assigned to the Assignee of the instant Application and the disclosures of each incorporated fully herein.
Known Nb-silicide based composites, including silicide-based RMIC materials, that exhibit adequate oxidation resistance characteristics for turbine component applications comprise compositions with the following approximate atomic percent ranges: Ti: 20-25, Hf: 1-5, Ta: 0-2, with a concentration ratio value (Nb+Ta):(Ti+Hf) of about 1.4, Si:18-21, Ge: 2-6, B: 2-5, with 22 less than (Si+Ge+B) less than 25, Cr: 10-14, Fe: 0-4, with 10 less than (Cr+Fe) less than 18, Al:0-4, Sn: 0-3, W: 0-3. Known Nb-silicide based composites, including silicide-based RMIC materials, that exhibit adequate creep-rupture resistance for turbine component applications comprise compositions with the following approximate atomic percent ranges: Ti: 16-20, Hf: 1-5, Ta: 0-7, with a concentration ratio value (Nb+Ta):(Ti+Hf) of about 2.25, Si: 16-19, Ge: 0-6, B: 0-5, with 17 less than (Si+Ge+B) less than 21, Cr: 6-10, Fe: 0-4, with 6 less than (Cr+Fe) less than 12, Al:0-4, Sn: 0-3, W: 0-3, Mo: 0-3. Further, known Nb-silicide based composites, including silicide-based RMIC materials, that exhibit adequate fracture toughness for turbine component applications comprise greater than or equal to about 30 volume percent of metallic phases.
The above Nb-silicide based composite and silicide-based RMIC materials comprise small overlapping ranges of constituents, in which the overlapping regions are small in size. Thus, a single silicide-based RMIC material composition is not readily available in which the RMIC can provide adequate creep, oxidation and toughness resistance for turbine component applications is very difficult to obtain.
While the oxidation performance and creep-rupture resistance for turbine component applications of known RMICs are desirable, these materials still may be improved for turbine component applications. For example, the chemistries and compositions of the RMIC material may be enhanced to enhance oxidation resistance and creep resistance for applications that subject the turbine component to high stresses at elevated temperatures in a range from about 2000xc2x0 F. to about 2400xc2x0 F. over long periods of time.
Therefore, a need exists to provide a material with a composition and chemistry for applications over long periods of time and under high stresses at elevated temperatures. Further, a need exists to provide a RMIC for turbine component applications with enhanced oxidation resistance and creep resistance over long periods of time and under high stresses at elevated temperatures.
Accordingly, one aspect of the invention provides a refractory metal intermetallic composition comprising, in atomic percent, titanium (Ti) in a range from about 17% to about 23%, hafnium (Hf) in a range from about 1.2% to about 3%, silicon (Si) in a range from about 16% to about 183%, 2% aluminum (Al), chromium (Cr) in a range from greater than about 6% to about 10%, germanium (Ge) in a range from about 2% to about 4%, 2% tin (Sn), iron (Fe) in a range from about 2% to about 4%, and a balance of niobium (Nb). The refractory metal intermetallic composition may further comprise at least one of boron (B), tantalum (Ta), and tungsten (W). The refractory metal intermetallic composition may contain at least one of 2 atomic percent boron (B), 5 atomic percent tantalum (Ta), and 3 atomic percent tungsten (W).
Another aspect of the invention comprises a turbine component that is formed of a refractory metal intermetallic composition. The refractory metal intermetallic composite comprises, in atomic percent, titanium (Ti) in a range from about 17% to about 23%, hafnium (Hf) in a range from about 1% to about 3%, silicon (Si) in a range from about 16% to about 18%, 2% aluminum (Al), chromium (Cr) in a range from about 6% to about 10%, germanium (Ge) in a range from about 2% to about 4%, 2% tin (Sn), iron (Fe) in a range from about 2% to about 4%, and a balance of niobium (Nb). The refractory metal intermetallic composition may further comprise at least one of boron (B), tantalum (Ta), and, tungsten (W). The refractory metal intermetallic composition may contain at least one of 2 atomic percent boron (B), 5 atomic percent tantalum (Ta), and 3 atomic percent tungsten (W).
A further aspect of the invention sets forth a multi-piece turbine component. The turbine component comprises a core and a surface layer. The turbine component surface layer comprises a refractory metal intermetallic composition comprising, in atomic percent, 23% titanium (Ti), 1.2% hafnium (Hf), 18% silicon (Si), 2% aluminum (Al), 10% chromium (Cr), 4% germanium (Ge), 2% tin (Sn), 4% iron (Fe), 2% boron (B), and a balance of niobium (Nb). The turbine component core comprises a refractory metal intermetallic composition that comprises, in atomic percent, 17% titanium (Ti), 3% hafnium (Hf), 16% silicon (Si), 2% aluminum (Al), 6% chromium (Cr), 2% germanium (Ge), 2% tin (Sn), 2% iron (Fe), 5% tantalum (Ta) and 3% tungsten (W), and a balance of niobium (Nb).